package 比赛.赛氪.test;

import java.util.Scanner;

public class test4 {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int[] res = new int[n];
        int[] res2 = new int[n];
        res[0] = 1;
        res2[0] = 1;
        for (int i = 1; i < n; i++) {
            res[i] = i + 1 + res[i - 1];
            res2[i] = res[i] + res2[i - 1];
        }
        System.out.println(res2[n - 1]);

    }
}
